In semiconductor manufacturing, automatic test equipment (ATE) is used to test integrated circuit (IC) devices, e.g., to characterize electrical properties, detect abnormalities, and evaluate product quality. During testing operations, stimulus signals are generated and provided to devices under test (DUTs) and the resultant output signals generated from the DUTs are evaluated against the expectation values.
A variety of standard IC tests require using a continuous wave (CW) RF signal having different power levels as the stimulus signal to a DUT, such as the gain and linearity tests for RF amplifies. Conventionally, varying the output level of an RF signal generator is accomplished by changing the internal state of the generator. In a typical RF generator, an automatic level control (ALC) feedback loop, in conjunction with an amplitude modulator and a variable attenuator, are used to ensure delivery of accurate signal levels to a DUT.
However, the utilization of the feedback loop inevitably and disadvantageously prolongs the transition time from one RF output level to another in terms of power, frequency, or amplitude, etc. For instance, in a linearity test on an RF power amplifier, it requires a power sweep across a given range. Commonly, the time it takes to switch an RF output in power or frequency is around 1 ms, and the time it takes to perform a test at one power level is around 20 μs. So, to measure over a 20 dBm range, the theoretical best time one can achieve is 20×(1.0+0.02) ms=20.4 ms. This demonstrates that the test throughput is predominantly limited by the transition times for switching of RF output levels, which leads to undesired increases in device manufacturing time and cost.